Unless Earth is special beyond reason, you can confidently assume there are plenty of societies out there. That doesn't mean that they'll come to Earth (or, as many believe, already have). Interstellar travel, despite what you've seen at the local multiplex, is hard. But we could easily get in touch via radio signals or flashing laser lights.
Majestic 12 is the name of an alleged organization created by President Truman to manage UFO and extraterrestrial investigations and maintaining strict secrecy in these areas. Many believe they have gone so far as to kill to keep secrets regarding interactions with the U.S. government and extraterrestrial civilizations.